JP2002036487A - Plate making method of thermosensible stencil paper, plate making apparatus, and stencil printing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a perforation form with the dispersion of shapes reduced while the size of the perforations of the film of thermosensible stencil paper by controlling the lowering of heat transfer efficiency by the influence of a profile and without requiring high temperature conditions to a plate making device. SOLUTION: In a plate making method of the paper in which independent dot-shaped perforations corresponding to an image are formed by selectively heating the heat shrinkable film of the base paper having the film by a heating device, the perforation has a profile enclosing a through hole, and the height h in relation to the film surface before perforation of the profile upheaving to the side facing a heating element on the film meets formulas [1] and [2] of h<=4 [μm] [1] and h<=0.05√(pxpy) [μm] [2].

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for making a heat-sensitive stencil sheet, which comprises perforating a film of a heat-sensitive stencil sheet used for stencil printing with a heating device such as a thermal head, and an apparatus obtained therefrom. Regarding stencil printing plates, in particular, to maintain the size of the perforations appropriately, without reducing the heat transfer efficiency and requiring large applied energy and high temperature conditions to the stencil making device, and to rely on random or image patterns. The present invention relates to a perforation mode having advantages such as suppressing variation in the shape of perforations that occur locally and preventing resin of a film from sticking to a heating element.

[0002]

2. Description of the Related Art Thermoplastic resin film of heat-sensitive stencil paper (hereinafter "thermoplastic resin film" is simply referred to as "film").
) Has the property that holes are formed for the passage of ink by receiving heat from a heating device such as a thermal head or a laser. During printing, ink is transferred to the paper through the perforations. Various materials for the film have been proposed so far, including polypropylene, polyamide, polyethylene, and vinyl chloride / vinylidene chloride copolymers in JP-A-41-7623, and propylene-based copolymers in JP-A-47-1184. Coalescence, in JP-A-47-1185, chlorinated polyvinyl chloride,
In JP-A-47-1186, highly crystalline vinyl chloride is used.
No. 6566 is a propylene-α-olefin copolymer, and in JP-A-49-10860, an ethylene-vinyl acetate copolymer is
Japanese Patent Application Laid-Open No. 51-2512 discloses an acrylonitrile resin, and Japanese Patent Application Laid-Open No. 51-2513 discloses a polyethylene terephthalate.
No. 669893 discloses polyvinylidene fluoride, and Japanese Patent No. 2030681 discloses a polyethylene naphthalate copolymer. At present, the heat-sensitive stencil film currently put to practical use in the market mainly includes the perforation sensitivity (performance of obtaining a perforation of a sufficient size with a small amount of heat) and mechanical aptitude (wrinkles at the time of plate making and printing, A heat-shrinkable film obtained by biaxially stretching polyethylene terephthalate or a vinylidene chloride-based copolymer is generally used because of its ability to prevent sagging, elongation and deformation. Polyethylene terephthalate is mainly used for printing machines.

On the other hand, in order to form perforations by heat,
Instead of the stretched heat-shrinkable film, a film obtained by casting a resin having a low melting point may be used. Patent 16
68117 and JP-A-62-173296 discloses a film cast from a solution or an emulsion of a synthetic resin.
No. 590 proposes a cast thermoplastic resin film containing silicone oil. In the case of a cast film, it does not exhibit heat shrinkage, but uses a resin having a low melting point, so that a heated portion is melted to cause perforation (hereinafter, this film is referred to as a “heat-meltable film”).

However, this hot-melt film is
It has not been commercialized as a heat sensitive stencil sheet in the market. It is considered that the reasons are mainly low perforation sensitivity, instability of perforation shape, and insufficient mechanical strength during printing of a plate-making product.

The heat-shrinkable film of heat-sensitive stencil paper for stencil printing presses currently in practical use has achieved a thickness of about 1.5 to 3 μm, and is claimed in Japanese Patent No. 1668117.
The difficulty of stably forming and laminating a film of μm or less has disappeared.

[0006] The movement of the resin in the perforation behavior is based on the fact that the heat-shrinkable film relies on a heat shrinkage stress that is sufficiently larger than the surface tension, whereas the heat-meltable film relies on only the surface tension. If the thickness and the melt viscosity are approximately the same, the heat-shrinkable film is much more sensitive than the heat-meltable film, that is, a sufficiently large perforation can be obtained with a small amount of heat.

[0007] The heat shrinkage stress of the heat shrinkable film has a clear temperature dependency, and as a result, perforations faithful to the temperature pattern obtained by the heating element of the thermal head are obtained. On the other hand, when a hot-melt film is heated and perforated by its surface tension, the temperature pattern of the heating element is not faithfully reflected in the perforated shape. This is because the direction in which the resin whose viscosity has decreased due to melting is moved by the surface tension is not limited to the direction of low temperature far from the center of the heating element, but may be gathered around the support fiber or slipped due to relative movement with the heating element. This is because they may be washed away irregularly. Therefore, even if a heat-sensitive stencil sheet using a hot-melt film is made into a stencil to realize a porosity suitable for printing conditions, the similarity of individual perforations is very low. In other words, microscopically, large holes and small holes are mixed, and it is difficult to realize a uniform density in a solid portion or the like of an image.

Further, although the resin of the heat-meltable film has a low melting point, it has a small area (pixel density of 300 to 600 dpi) and a short time (sub-scan cycle of 2 In order to obtain sufficient movement of the resin due to surface tension under conditions such as ~ 4 ms), it is necessary to apply a much higher temperature to the heating element than to the heat-shrinkable film, which causes the heating element to overheat and deteriorate. This can cause

Further, the heat-sensitive stencil sheet during printing is subjected to stress due to misalignment with the printing paper in the rotation direction of the plate cylinder. Heat-sensitive stencil paper using a cast hot-melt film,
Generally, the elastic modulus and the breaking strength are lower than those of a heat-sensitive stencil sheet using a stretched heat-shrinkable film. For this reason, the heat-sensitive stencil sheet provided with the heat-fusible film is more liable to cause deformation of a printed image and, in some cases, image contamination due to cutting of the base sheet, than the heat-sensitive stencil sheet provided with the heat-shrinkable film.

For the above reasons, heat-sensitive stencil paper is
It can be said that those having a heat-shrinkable film are the mainstream at present and in the future. Accordingly, the following discussion of heat-sensitive stencil paper is limited to heat-sensitive stencil paper with a heat-shrinkable film.

The heat-sensitive stencil sheet is used for the purpose of avoiding elongation, wrinkles (these cause distortion of a printed image), and breakage (which stains the printed image) due to the force received when the printing stencil sheet is set in a printing machine and performs a printing operation. Usually, in order to give a necessary strength, a structure in which a porous support is attached to the film described above is often used. The porous support has a structure that imparts strength to the heat-sensitive stencil sheet and satisfies the function of the stencil printing plate to allow ink to pass through the apertures. As the material of the porous support, (1) so-called Japanese paper made from natural fibers such as Kouzo, Mitsuma and Manila hemp, and (2) recycled fibers and synthetic fibers such as rayon, vinylon, polyester and nylon into paper form (4) a mixed sheet made by mixing the natural fiber of (1) with the recycled fiber or the synthetic fiber of (2);
There is known a so-called polyester paper obtained by mixing a polyester fiber with an undrawn polyester fiber as a binder fiber and subjecting the tissue paper to hot-press processing with a hot roll.

On the other hand, a heat-sensitive stencil sheet having such a structure in which a film and a porous support are bonded together realizes strength enough to withstand the force of the printing operation of a printing machine. In addition, when the ink passes through the heat-sensitive stencil sheet, unevenness of the ink permeability caused by the dispersion state of the fibers of the porous support (which may reduce the uniformity of the density of the printed image) may occur. To avoid this, a proposal has been made to make the heat-sensitive stencil paper substantially a single-layer structure of a film.

As a method of making a plate by forming perforations in the film of the heat-sensitive stencil sheet, the film side of the heat-sensitive stencil sheet is brought into close contact with a document having an image portion containing carbon to irradiate infrared rays to the image portion. A method of perforating a film by heat generation of a heat-sensitive stencil, a method of closely moving a film side of a heat-sensitive stencil sheet and a thermal head and moving the heating element corresponding to an original image to perforate the film, For example, there is a method of perforating a film by scanning a modulated laser beam corresponding to a document image. Of these methods, the method using infrared rays has a limitation on the type of original and cannot cope with data editing of documents and images. The laser method has not been put to practical use mainly due to the length of the plate making time. Therefore, at present, the method using a thermal head is mainly used.

In plate making using a thermal head, a large number of perforations are formed two-dimensionally arranged in the main scanning direction and the sub-scanning direction. At this time, it is desirable that the perforations have substantially the same shape and realize an opening ratio suitable for printing conditions. This is because if the perforated shapes are uniform, the microscopic ink transfer state is uniformed in the image area, particularly in the solid area, and a uniform density can be obtained. Conversely, if the perforation shape is irregular, the microscopic ink transfer state is not constant, the thin lines are blurred, the solid density is uneven, or the ink transfer is partially excessive due to excessive perforation. Will cause set-off. For this reason, various proposals have been made regarding the shape of the heating element in order to stabilize the shape of the hole formed by each heating element. In Japanese Patent No. 2732532, the pitch of the main scanning and the pitch of the sub-scanning are equal, the length of the heating element in the main scanning direction is shorter than the length of the sub-scanning direction, and the length of the heating element in the sub-scanning direction is smaller than the pitch of the sub-scanning. There has been proposed a method of shortening the length to obtain independent perforations in both the main scanning direction and the sub-scanning direction. Japanese Patent Application Laid-Open No. 4-314552 proposes a method in which a cooling member using a material having high thermal conductivity is arranged between heating elements adjacent in the main scanning direction to prevent connection of perforations adjacent in the main scanning direction. . Japanese Patent Application Laid-Open No. Hei 6-15042 discloses that a heat-sensitive stencil sheet made of a thermoplastic resin film alone has a length in the main scanning direction of a heating element within a range of 15 to 75% of a pitch of a main scanning, and a length in a sub-scanning direction of the heating element. There has been proposed a method of making a plate using a thermal head in which the pitch is set within a range of 15 to 75% of the pitch of the sub-scan.

Conventionally, regarding the perforation form, the planar shape (diameter, aspect ratio, area) of the perforation or its statistical state (average value, variation) has been exclusively discussed, and the perforation of the perforation which gives a desirable ink transfer state has been discussed. Almost no mention is made of the contour shape except for the following examples. That is, in Japanese Patent No. 2638390, the relationship between the length of the heating element in the main scanning direction and the length in the sub-scanning direction and the length of the hole in the main scanning direction and the length in the sub-scanning direction is defined. Methods have been proposed for obtaining perforations that are also independent in the direction, in which the presence of perforations is described. JP-A-6-320700 discloses a method in which a heat-sensitive stencil sheet consisting essentially of a film is heated from one side by a first thermal head, and then heated from the other side by a second thermal head and perforated. A cross-sectional shape of the perforation is described therein. In JP-A-8-20123, in order to remove variations in perforated shape caused by the support of the heat-sensitive stencil sheet, the heat-sensitive stencil sheet is substantially composed of only a thermoplastic resin film having a thickness of 3.5 μm or more, and formed. The perforated hole has a mortar-shaped cross section, and a plate making method of heat-sensitive stencil paper in which the size of the mortar cross section is defined in relation to the pitch of main scanning has been proposed.

Patent No. 2732532, JP-A-4-314552,
Japanese Patent Application Laid-Open No. Hei 6-15042 is a powerful method for preventing enlargement due to the connection of adjacent perforations, aligning individual perforations, and achieving a desired ink transfer state, but the perforation behavior depends on the physical properties of the film. For this reason, it cannot be said that it shows the best way to control the perforation shape for various heat-shrinkable films.

Also, the above-mentioned Japanese Patent No. 2638390, Japanese Patent Laid-Open No. 6-32070
No. 0 describes the outline of the drilling and the cross-sectional shape of the drilling, but they only indicate its existence, and the effect of the drilling outline and cross-sectional shape on the drilling shape and the heat transfer efficiency are reduced. There is no suggestion about a method for preventing the perforation or a method for making the perforated shape uniform.

Further, in the plate making method described in JP-A-8-20123, the relationship between the dimensions of the mortar cross section and the pitch of the main scan is specified as described above. Heat-sensitive stencil paper consisting solely of a thick thermoplastic resin film without a support is not currently implemented as a product on the market, and the problem before its perforated form has not been solved. In addition, it does not mention the cross-sectional shape of perforations made in general thermosensitive stencil paper, including the conventional form in which a thermoplastic resin film and a porous support are bonded together, and does not refer to the cross-sectional shape or height of the contour. Does not disclose any finding that the influence of the influence on the heat transfer efficiency and the variation of the perforated shape.

[0019]

SUMMARY OF THE INVENTION In a stencil printing plate,
When trying to form a through hole of a certain size, the resin in the part perforated by the thermal head moves to the outline around the through hole, but the thermal properties of the film of the heat-sensitive stencil paper and the heat generated by the thermal head Depending on the heat generation conditions of the element, the resin accumulated on the contour is often formed to be larger than the surface of the film to be heated.

The raised portion is interposed between the surface to be heated of the film and the heating element of the thermal head, and serves to separate the surface to be heated of the film from the heating element. As a result, it is difficult to greatly reduce the efficiency of heat transfer from the heating element to the film and to achieve the target size of the through hole. If the size of the through hole does not reach the target value, the density of the printed matter is insufficient. On the other hand, if an attempt is made to achieve the target value by increasing the energy applied to the heating element of the thermal head, the heating element may be damaged.

On the other hand, the distance that the formed protrusion separates the heated surface of the film from the heating element is different between a non-image portion where no perforations are formed and a solid portion where a large number of perforations are formed. Therefore, the above-described decrease in the heat transfer efficiency is affected by the image ratio, and causes uneven density in the printed matter. In addition, since the raised portion of the contour is pressed against the heating element of the thermal head and conveyed by shearing force, the planar shape of the contour of the perforated hole, that is, the shape of the through hole is distorted, and the printed material is microscopically printed. This causes a reduction in the reproducibility of patterns such as uneven density and characters. When the shape of the through-hole is significantly distorted, the through-holes of adjacent perforations are connected to each other, thereby causing set-off due to transfer of an excessive amount of ink from the large through-hole to paper.

Furthermore, the resin of the film deformed by the above-mentioned shear falls off the film and deposits on the downstream side of the heating element of the thermal head, which further reduces the plate making performance by further separating the heating element from the film. May cause symptoms.

It has been known that the causes of these symptoms are due to the thermophysical properties of the film and the heat generation conditions of the heating element of the thermal head. However, in relation to the height of the contour protruding around the through hole of the perforation, it is known. It was not picked up. Also,
Specific knowledge about the factors that determine the perforation shape, including the perforation outline, was not clarified, and was in a state of trial and error.

The present invention has been made to solve this problem, and suppresses the heat transfer efficiency due to the influence of the contour, and does not require a large applied energy and a high temperature condition for the plate making device. Perforation forms for maintaining the size of the holes appropriately, suppressing variations in the perforations that occur randomly or locally depending on the image pattern, and preventing the resin of the film from sticking to the heating element. The purpose is to provide.

[0025]

The inventor of the present invention has conducted intensive studies on the perforation behavior of heat-sensitive stencil paper under the above-mentioned object, and has found that the perforation is performed so that the height of the contour conforms to a certain condition according to the pitch between the perforations. It has been found that the formation suppresses variation in the shape of the perforations regardless of the thickness and melting point of the film, thereby obtaining a good printed matter.

That is, according to the first aspect of the present invention, the heat-shrinkable film of the heat-sensitive stencil sheet provided with the heat-shrinkable film is selectively heated by a heating device to form an independent dot corresponding to an image. In the plate-making method for forming a perforation, the perforation has a contour surrounding the through-hole, and a height h of the contour rising on the surface on the heated side on the heat-shrinkable film with respect to the film surface before perforation is as follows. equation [1] and the formula the process for making a heat-sensitive stencil sheet which satisfies the [2], h ≦ 4 [ μm] [1] h ≦ 0.05√ (p x p y) [μm] [2] ( wherein, p _x main scanning pitch [μm], p _y is the sub-scanning pitch [[mu] m].) is provided.

Further, according to the second aspect of the present invention, the heat-shrinkable film of the heat-sensitive stencil sheet provided with the heat-shrinkable film is selectively heated by a heating device to form an independent dot corresponding to an image. In a plate making apparatus for forming a perforation,
The perforation has a contour surrounding the through-hole, and the height h of the contour raised on the surface on the heated side on the heat-shrinkable film with respect to the film surface before perforation is represented by the following formulas [1] and [2]. plate making apparatus of the heat-sensitive stencil sheet which satisfies the, h ≦ 4 [μm] [ 1] h ≦ 0.05√ (p x p y) [μm] [2] ( wherein, the p _x main scanning Pitch [μm], _py is the sub-scanning pitch [μm]).

According to the third aspect of the present invention, there is provided a stencil printing plate provided with a heat-shrinkable film in which independent dot-like perforations corresponding to an image are formed by being selectively heated by a heating device. The perforation has a contour surrounding the through hole, and the height h of the contour rising on the surface on the heated side on the heat-shrinkable film with respect to the film surface before perforation is represented by the following formula [1] and formula stencil printing plate, characterized by satisfying the [2], h ≦ 4 [ μm] [1] h ≦ 0.05√ (p x p y) [μm] [2] ( wherein, the p _x main scanning Pitch [μm], _py is the sub-scanning pitch [μm]).

According to a fourth aspect of the present invention, there is provided a heat-sensitive stencil sheet provided with a heat-shrinkable film which is selectively heated by a heating device to form independent dot-like perforations corresponding to images. The perforation has a contour surrounding the through hole, and the height h of the contour rising on the surface on the heated side on the heat-shrinkable film with respect to the film surface before perforation is represented by the following formula:
[1] and the heat-sensitive stencil sheet which satisfies the formula [2], h ≦ 4 [ μm] [1] h ≦ 0.05√ (p x p y) [μm] [2] ( wherein, p _x is the pitch of the main scan [μm], and _py is the pitch of the sub-scan [μm].

Hereinafter, the present invention will be described in detail.

As described above, there are two types of heat-sensitive stencil paper, from the structure thereof, those having a structure in which a film and a porous support are bonded to each other, and those having a substantially single-layer structure of a film. The following discussion is independent of the composition of such heat-sensitive stencil paper, the desired perforation features to be made in the film of heat-sensitive stencil paper, the plate making method for forming perforations having such shape characteristics, plate making apparatus,
Since it relates to the properties of the heat-sensitive stencil paper and the prepress-formed heat-sensitive stencil paper obtained therefrom,
In the case of heat-sensitive stencil paper, both those having a structure in which a film and a porous support are bonded together and those having a substantially single-layer structure of a film are generically referred to, and are not particularly distinguished. In fact, the present invention can be applied to both of the above two types of heat-sensitive stencil sheets. Hereinafter, a heat-sensitive stencil sheet made for stencil printing is referred to as a "stencil printing plate".

Generally, perforations 1 formed in a film of a heat-shrinkable heat-sensitive stencil sheet are composed of a penetrating portion 2 and a deformed portion 3 formed therearound as shown in FIG. . This penetrating portion 2 is hereinafter referred to as “through hole”. The deformed portion 3 formed around the through hole 2 has a thickness changed compared to the film before plate making. The deformed portion 3 generally comprises an elliptical cross-section portion (this portion is referred to herein as a "contour") 4 and, in some cases, a thin film portion 5 that contacts the inside. The volume of the thin film portion 5 is very small compared to the volume of the outline 4. Depending on the conditions of the film or plate making, the thin film portion 5 may not be formed. The outline 4 is thicker than the state before plate making or a part that is not deformed by plate making. In the present specification, the film surface 6 on the side heated by the heating device of the heat-sensitive stencil sheet before the stencil making or the portion not deformed by the stencil making is referred to as “reference plane”
Call it. The maximum height 7 at which the contour 4 rises relative to the reference plane 6 in the direction of the heating device is defined herein as the "height" of the contour. Also, the through hole 2 and the deformed portion 3
In this specification, the entirety 1 combined with is referred to as “perforation”.
Forming the perforations 1 is also referred to as "perforating" in this specification.

The present inventors have found a method for evaluating the perforation phenomenon from a new viewpoint which has not been seen in the past, in a study on the present invention. In other words, using a device that can rapidly image the phenomenon of heat shrinkable film perforation by a thermal head, which is currently the most common thermal stencil sheet making method, in a micrometer order microscopic field of view in the order of microseconds, and perforate the film with time. Was observed and the behavior of expansion was observed. Thus, it was found that a series of perforation behaviors was divided into the following four stages.

First, a voltage is applied to the heating element, and Joule heat is generated. As a result, as shown in FIG. 2, the heating element of the thermal head has a temperature distribution in which the temperature is highest at the center and lowers toward the periphery, and heats the film. Thereby, the film becomes as shown in FIG.
The portion in contact with the center of the heating element has the highest temperature, and the farther away from it, the lower the temperature. Of course, both the temperature distribution of the heating element and the temperature distribution of the film change with time.

As shown in FIG. 4, when the film exceeds a temperature 8 at which shrinkage starts (hereinafter referred to as “shrinkage start temperature”, the shrinkage start temperature 8 exceeds the glass transition temperature of the film). Since a force (heat shrinkage stress) is generated in the direction of the surface to reduce the distance, the shrinkage start temperature 8
Tension is generated throughout the above area. The direction of the resultant of the tensions is substantially perpendicular to the isotherm on the film (if thermal shrinkage is isotropic, completely). On the other hand, where the temperature of the film is lower than the glass transition temperature, the resin of the film does not move, and where the temperature of the film exceeds the glass transition temperature, the higher the temperature, the more easily the resin deforms. It moves toward the periphery, that is, sliding down the slope of FIG. In FIG. 5, the distribution of the temperature of the film (isothermal line) when the heating elements adjacent to each other in the main scanning direction generate heat is indicated by a solid line, and the direction in which the temperature decreases perpendicular to the isothermal line is indicated by a dotted arrow. That is,
The resin of the film moves in the direction of the dotted line in FIG.

Second, the first small through-holes occur near the hottest part of the film (the occurrence of perforations).

Third, the outer periphery of the small through hole generated is
It is pulled toward the periphery by the tension from the outside (growth of perforations due to heat shrinkage). While the outer periphery of the through hole is pulled toward the peripheral portion, the volume in the resin is increased by taking in the resin along the path to form a contour.
The cross-sectional shape of the contour takes a shape close to a circle or an ellipse due to surface tension.

In general, when the heat-shrinkable film is kept in a temperature range where the heat-shrinkage behavior is exhibited, the heat-shrinkable behavior eventually does not exhibit the heat-shrinkage behavior. At the stage of perforation growth, the contour is considered to be in a state in which the heat shrinkage has been completed, consisting of a molten or softened resin. Therefore, when there is a perforation of an adjacent pixel such as a solid portion, if the outlines of the adjacent perforations come into contact with each other due to the growth of the perforation and merge, a portion that pulls the outline outward, that is, the heat shrinkage is over. Since there are no missing parts, the contour cannot grow any more perforations by heat shrinkage.

However, for example, in the case where the size of the transferred image to paper is not sufficient for the largest through-hole which is expanded by thermal shrinkage, that is, when the dot gain is small, a printed matter having no gap between pixels is obtained. For this purpose, it is necessary to increase the size of the through hole, and the heating may be continued. At this time, the perforations do not grow due to heat shrinkage, but the outline is heated and sufficiently softened, and the perforations move due to surface tension. This is shown in FIG. Movement due to surface tension occurs from a low-viscosity portion (a high-temperature portion between adjacent through holes) to a high-viscosity portion (a low-temperature portion between diagonally adjacent through holes). growth). However, there is a portion where the heat shrinkage is not finished between the diagonally adjacent through holes, and the through hole further expands in the direction of the diagonally adjacent through hole due to the heat shrinkage (white in FIG. 6). Bold arrow).

Fourth, when the temperature of the heating element drops after the application of the voltage to the heating element, and then the temperature of the film also decreases, the temperature of the contour and the outer part thereof becomes the contraction start temperature.
Below 8, the contour can no longer be pulled towards the periphery. Further, as the temperature of the contour decreases, the viscosity increases, and the movement due to surface tension stops. With these, the shape of the perforation is fixed (end of perforation).

At present, the surface roughness of the film surface of a general heat-sensitive stencil sheet commercially available for a heat-sensitive stencil printing machine is as follows:
The arithmetic average roughness Ra is about 1 to 1.5 μm, and the 10-point average roughness Rz is about 3.5 to 5 μm. These values were measured by a non-contact three-dimensional shape measuring device NH-3 manufactured by Mitaka Optical Co., Ltd.
mm × 10 mm area, vertical and horizontal pitch of 30 μm, the cut-off wavelength is 2.5 mm, and the film surface of the heat-sensitive stencil paper tensioned on a plane is measured in an open (no pressure applied) state, It is not the one that is nipped by the thermal head and the platen roller during actual plate making. The surface roughness of the film surface of the heat-sensitive stencil paper in the nip state is considered to be smaller than the value in the open state, but a reasonable method for directly measuring or estimating this is as follows.
Not yet obtained.

At present, a thermal head used in a stencil printing machine generally has a thin film type formed by a sputtering process. The morphological feature near the heating element of the thin-film thermal head is that the surface of the heating element is
That is, it is recessed by about 1 μm from the surface of the electrode portion adjacent in the sub-scanning direction. The surface of the electrode part of the thermal head is closest to the film side of the heat-sensitive stencil paper, the arithmetic average roughness Ra is about 0.1 μm or less, and the 10-point average roughness Rz is 0.
It is about 2 μm.

The distance d ₀ [μm] between the film surface of the heat-sensitive stencil sheet and the surface of the heat generating element of the thermal head in the nip and non-perforated state is not a reasonable estimate, Dent h, 10-point average roughness R _zt of the surface of the electrode portion near the heating element of the thermal head, and 10-point average roughness R _zf of the film surface of the heat-sensitive stencil paper.

[0044]

(Equation 1)

The degree can be expected. According to this assumption, d ₀ is

[0046]

(Equation 2)

Is as follows.

When the film of the heat-sensitive stencil sheet at the portion nipped by the thermal head and the platen roller is not perforated at all, the height of the contour is zero. Therefore, the distance d ₀ [μm] between the film surface, that is, the reference surface, and the surface of the heating element in contact with the film surface immediately before the first perforation occurs in this portion depends on the shape or surface roughness of both in the nip state. And, as already mentioned,

[0049]

(Equation 3)

The degree can be assumed.

However, when the film is perforated by plate making, the perforation grows at the same time as the third stage of the perforation behavior described above, and at the same time, the contour of the perforation occurs, and the cross-sectional area increases. That is, the contour is raised. The raised portion of the contour is close to the heating element. Therefore, the raised portion of the contour is sandwiched between the reference surface and the heating element.

When the heating element is located in the sub-scanning position after the leading end of the image area, that is, the portion of the heat-sensitive stencil sheet that is nipped by the thermal head and the platen roller, which has passed through the heating element. Is already perforated, the contour of the raised perforation in the already perforated portion is sandwiched between the reference plane and the vicinity of the heating element.

The influence of these appears as one of the following two phenomena or both at the same time.

The first phenomenon is that a portion that pulls the outline outward is farther from the heating element by the height of the outline than the most prominent portion of the outline.

Precisely, as already mentioned, since the contour during the growth of the perforations is a molten or softened resin, the contour may be somewhat crushed by the nip pressure. Further, by observing the perforated heat-sensitive stencil sheet with a microscope, it is possible to confirm the contour of the perforated hole that has been crushed and deformed. According to the observation, the contour of the perforation may be deformed in the above-mentioned convex portion of the surface roughness of the film surface and in the image portion where the support fiber is in contact with the back surface. The height of the deformed contour is not always zero, but varies over a wide range from 0 to 100% of the height before deformation. The variation in the contour deformation indicates that the pressure applied to the deformed portion varies and that the contour of the perforation has such a hardness that the height does not become zero with respect to the applied pressure.

Further, on the film passing through the heating element,
The contour of the already perforated part quickly cools and hardens,
Thereafter, the contour height does not deform even when subjected to the nip pressure. The distance between this contour and the heating element in the sub-scanning direction is 100 μm
When the temperature is within the range, the contact between the surface of the heating element and the surface of the film on which the heating element is to be pierced, that is, the reference surface is prevented.

Therefore, in most of the perforated portions of the image portion, the minimum value of the distance between the surface of the heating element and the reference surface is increased by the height of the contour. If the height of the contour is α [μm], then the distance d between the reference plane and the surface of the heating element
[Μm]

[0058]

(Equation 4)

The degree can be assumed. Here, β [μm]
Indicates an increase in the maximum value of the distance between the surface of the heating element and the reference plane due to the occurrence of the contour. α and β are

[0060]

(Equation 5)

It is considered that The temperature of the portion where the contour is pulled outward is lower than when the height of the contour is not affected. That is, there is a problem that the heat transfer efficiency is reduced. The degree is more remarkable as the height of the contour is higher. This terminates the third perforation process early and stops perforation growth.

In the state where the height of the contour is high and the heat transfer efficiency is low, if a sufficient amount of heat is not given to the heat generating element, the size of the perforations does not reach the target value, and the density of the printed matter decreases. .

In a state where the height of the contour is high and the heat transfer efficiency is low, if a sufficient amount of heat is applied to the heat generating element to realize the target size of perforation, the power consumption during plate making increases. Also,
If the application conditions are set by increasing the application time, the plate making time generally increases. Furthermore, when the temperature of the heating element is set high during plate making, the time required for the heating element to reach a certain temperature or higher is lengthened, and the heating element is likely to deteriorate. Originally, in the case of a thermal head widely used as a heating device for thermal plate making, the heat generation temperature range (300 to 400 ° C.) is limited to the use limit temperature (400 ° C.).
This trend is more pronounced because

As described above, the contour of the perforation that has passed through the heating element does not deform even when subjected to the nip pressure, and when the distance between the contour and the heating element in the sub-scanning direction is within about 100 μm, The heat transfer efficiency is reduced by preventing the close contact between the surface of the heating element and the surface of the film on which the heating element is to be perforated, that is, the reference surface. This phenomenon does not occur uniformly in the image, but depends on the pattern of the image. That is, the top portion of the image portion in the sub-scanning direction, the inside of the solid,
Alternatively, in each of the low image ratio portions such as the thin portion and the gray portion of the area gradation, the height of the contour formed at the immediately preceding sub-scanning position and the area of the contour receiving the nip pressure are different, and the height of the formed contour is different. If the distance is high, the distance between the surface of the heating element and the reference plane greatly changes depending on the location. Therefore, the size of the perforations varies depending on the location on the image, and the density of the printed matter locally varies. Therefore, this symptom cannot be compensated for by adjusting the average value of the transfer amount and the transfer density by controlling the viscosity of the ink, the color material ratio, and the printing pressure.

The second phenomenon is that the resin in the raised portion of the contour sandwiched between the reference surface and the heating element is considered to be in a state in which the heat shrinkage has ended and is in a state of being heated and softened or melted. It is crushed by the pressure of the time, and is further deformed by shear stress applied to the heating element.

The shape of the resin at the protruding portion of the contour is crushed and deformed, and has a variation. The reason is that, for each pixel or perforation, the heating state of the corresponding heating element is not completely uniform, the distance of heat transfer varies due to the surface roughness of the film, and the heat due to the location of the film. This is because variations in shrinkage physical properties and influence of the heat capacity of the dispersed support fibers cause variations in the perforated shape, resulting in variations in the volume, hardness, and shearing stress of the contour. When the height of the contour is high, the shape after the contour is deformed, that is, the variation in the final perforated shape is remarkable, and the contour is partially dropped and the adjacent perforations are connected or the crushed contour portion May partially or completely block adjacent perforations in the main scanning direction or the sub-scanning direction. When printing is performed using such a stencil printing plate, the variation in the amount of ink transfer in the image area increases. In particular, the solid portion has a rough feel, and the uniformity of density is reduced. At the same time, fainting and crushing of fine characters occur. Further, set-off and strike-through occur in a printed portion having a large transfer amount.

When the resin at the protruding portion of the contour is crushed and deformed, the resin of the film, the component of the adhesive for bonding the film to the porous support, and the like adhere to the heating element (burn). )Sometimes. The film is usually coated with a release agent to prevent sticking to the heating element. However, if the contour is high, the heating value of the heating element is increased in order to obtain a perforated hole of a desired size. Therefore, the temperature of the heating element increases. Furthermore, due to the high height of the contour,
The film and the heating element come into strong contact and receive shear stress.
As a result, the resin in the contour portion and the adhesive component incorporated in the contour portion are easily fixed to the heating element.

If the resin or the adhesive component in the outline portion adheres to the heating element itself, it is the same as a decrease in the amount of heat generated by the heating element, and the size of the perforation becomes small or the perforation becomes impossible. is there. In this case, the printed matter has insufficient density at the portion where the perforation is defective, or image loss at the portion where the perforation is impossible. Furthermore, if the area to be fixed is large, a large area of the film may fall off the support, and thus the printed matter may stick to the area downstream of the image area as if scratched (sticking). Naturally, this causes set-off and strike-through.

Even if the resin or adhesive component in the outline does not adhere to the heating element itself, it may be deposited little by little on the surface of the thermal head downstream of the heating element. The deposited resin is sticky and does not pose a major problem at first,
When the deposition amount increases over time, dust and dust adhering to the film surface are dammed immediately after the heating element,
The deposits become large, creating a distance between the heating element and the film, and the amount of heat transfer is insufficient, so that the size of the perforations may be reduced or the perforations may not be possible. In this case, the printed matter also has insufficient density at the portion where the perforation is defective, or image loss at the portion where the perforation is impossible.

When a heat-sensitive stencil sheet is made by a thermal head, as described above, a voltage is applied to the heating element, and Joule heat is generated. As a result, as shown in FIG. 2, the heating element of the thermal head has a temperature distribution in which the temperature is highest at the center and lowers toward the periphery, and heats the film. By doing so, the film
As shown in Fig. 3, the temperature at the portion where the center of the heating element is in contact is the highest, and the temperature decreases as the distance from the center increases. Of course, both the temperature distribution of the heating element and the temperature distribution of the film change with time.

How much energy can be applied to obtain a target size of through hole depends on the perforation sensitivity as the performance of the heat-sensitive stencil sheet and the heat transfer efficiency as the performance of the heat-sensitive stencil making apparatus.

At present, a heating element of a thin-film thermal head generally used in a stencil printing machine has aluminum as an electrode in a sub-scanning direction, and has an underlying layer (a direction opposite to the heat-sensitive stencil sheet). Is a ceramic as a heat insulating layer, and a glass as a protective layer is in contact with the upper layer (in the direction of the heat-sensitive stencil sheet). However, since the thickness of the protective layer is as thin as several μm, the heat capacity is very small as compared with the electrodes and the heat insulating layer. From the surface of the protective layer (this is referred to as “the surface of the heating element” in the description so far in this specification, and hereinafter, unless otherwise specified, it is used in this sense) from the thickness d [ μm], the heat is transferred to the film by:

[0073]

(Equation 6)

Here, α is the height of the contour, β is the increment of the maximum value of the distance between the surface of the heating element and the reference plane due to the occurrence of the contour,

[0075]

(Equation 7)

It is considered that The thermal conductivity [W m ^-1 K ^-1 ] of the above material in contact with the heating element is described in the literature (Science Table '9
According to the 8-year edition, edited by the National Astronomical Observatory of Japan, Maruzen), aluminum is 230-240, ceramic (porcelain) is 1.5, glass (quartz glass) is 1-2, and air is extremely small, 0.02-0.07. That is, if the thickness d of the air layer is slightly increased by α, the temperature of the film is greatly reduced, and as described above, the heat transfer efficiency is reduced. In order to avoid this, the thickness of the air layer, that is, the distance between the surface of the heating element and the reference plane must be as small as possible.

In order to reduce the thickness d of the air layer, it is necessary to reduce α in the above equation, that is, the height of the contour.

The allowable upper limit of the contour height α was examined by experiment. In the experiment, a film having a thickness of α as a spacer was applied to a position near the heating element of the thermal head so as not to interfere with the spread of perforations, and plate making was performed. Care was taken to avoid interference between the outline of the perforated plate making and the spacer film in the nip area. As a result, when the thickness α of the spacer film exceeds 4 μm,
Compared to the case where the spacer film is not applied, if the electrical settings of the thermal head are the same, the quality of the perforated shape (average and variation in the size of through holes, variation in shape) and the image quality of printed matter (image area It was found that the average value, the variation and the blurring of the density were greatly reduced. On the other hand, when the energy applied to the thermal head is increased to make the average value of the size of the through hole of the perforation coincide with the case where the spacer film is not attached, the average value of the size of the through hole of the perforation and the image area of the printed matter are obtained. The average value of the density was improved, but the quality of other perforated shapes (variation in the size and shape of the through-holes) and the image quality of other printed matter (variation in the density of the image area) also decreased. And it was set off, and strikethrough was greatly worsened.

Further, it has been found that the thickness α ₁ of the spacer film, which starts to affect the quality of the perforated shape and the image quality of the printed matter, changes depending on the resolution of the plate making. That is, 30
Α ₁ ≒ 4 μm at 0 dpi, α ₁ ≒ 3.2 μm at 400 dpi,
At 600 dpi, α ₁ was 2.2 μm. When the main scanning resolution is different from 300 dpi and the sub scanning resolution is different from 400 dpi, α
₁ ≒ 3.7 μm. The values of these alpha ₁ is equal to about 5% of the geometric mean of the pitch and the sub-scanning pitch in the main scanning. Good stencil sheet condition, that is, those degree of surface roughness of the film surface is small, if the above value alpha ₁ or less with respect to the thickness alpha respective resolutions spacer film, adhered to the spacer film Compared with the case where no thermal head was used, it was possible to obtain substantially the same quality of the perforated shape and the image quality of the printed matter even when the electrical settings of the thermal head were the same.

From the above, the present inventors set the contour height within a range not exceeding 4 μm in order to achieve the above object of the present invention, and furthermore, set the contour height in the main scanning direction. It was found to be set within a range not exceeding 5% of the geometric mean of the pitch of the sub-scan and the pitch of the sub-scan.

In order to set the perforation form in the scope of the present invention, it is necessary to optimize the height of the contour, and any method can be used. The height of the contour depends on the volume of the resin in the contour part and the oblateness of the cross section of the contour. The volume of the resin in the contour part depends on the volume of the resin at the location of the through-hole before drilling. That is, by selecting the thickness of the film while keeping the area of the through hole, the volume of the resin in the contour portion can be selected, and therefore, the height of the contour can be selected. In addition, by selecting the spatial distribution of the temperature of the heating device (for example, the shape of the heating element of the thermal head and the applied energy) and the temporal change (for example, the combination of the power applied to the thermal head and the application time), the outline of the contour can be obtained. The flatness of the cross section can be selected, and therefore the height of the contour.

The heating device described above includes:
Although the heating element of the thermal head is often mentioned as an example, the present invention can be applied to a general phenomenon of perforation by heating a heat-shrinkable film, so that the heating device is not limited to the thermal head, but may be a laser light source or an active energy. Sources and many other devices can be used.

[0083]

The present invention will be described below with reference to examples and comparative examples. Plate making conditions in each example and comparative example,
Table 1 shows the measured values of the perforation shape, the evaluation of the perforations, and the evaluation of the printed matter. In addition, the measuring method of the physical property shown in Table 1 is as follows. Hereinafter, the present invention will be described based on examples and comparative examples.

Evaluation conditions for plate-making products In each of the examples and comparative examples, the plate-making plate is an experimental plate-making apparatus and a heat-sensitive plate which meet the respective conditions (resolution, pitch, heating element size, applied energy, period, film properties) shown in Table 1. It was performed with stencil paper. The other common condition of the heat-sensitive stencil paper is that it is biaxially stretched using various polyester resins having different mixing ratios as materials.
A film having a thickness and a melting point shown in Table 1 was formed, and a mixed paper made of manila hemp and polyester fiber having a basis weight of 10 g / m ² and a thickness of 35 μm as a porous support was applied at a coating amount of 0.5 g / m 2.
After bonding through the polyvinyl acetate resin of No. ² , a silicone resin was applied to the surface of the film at 0.1 g / m ² to produce the film. The ambient temperature is room temperature.

Min {4, 0.05, (p _x p _y )} Indicates the smaller value of the right side of equation [1] or the right side of equation [2]. In the present invention, the height of the contour is particularly preferably equal to or less than this value.

The surface roughness of the film surface of the heat-sensitive stencil base paper The arithmetic average roughness Ra and the 10-point average roughness Rz were determined as the surface roughness of the film surface of the heat-sensitive stencil base paper by Mitaka Koiki Co., Ltd., non-contact tertiary. With the original shape measuring device NH-3, the film surface of the heat-sensitive stencil base paper, which is tensioned on a plane, is opened at a cut-off wavelength of 2.5 mm in an area of 10 mm long × 10 mm wide at a pitch of 30 μm both vertically and horizontally. (Not applied).
Arithmetic average roughness Ra and 10-point average roughness Rz are JIS B 0601
According to the definition of "Surface roughness-definition and indication".

A pattern in which the solid pattern is formed by making a solid pattern with the diameter of the through hole and the height of the contour, and the heat history state on the plate is the same (5 mm or more and 15 mm or less downstream from the plate making start line in the sub-scanning direction). The surface roughness of the perforation in
Laser Tech Co., Ltd. Scanning Laser Microscope 1LM21
The diameter of the through-hole and the height of the perforation in the main scanning direction and the sub-scanning direction were determined as an average in each of 20 perforations.

A pattern of the SN ratio solid pattern of the area of the through-hole is made into a plate, and in a region where the thermal history state on the plate is the same (5 mm or more and 15 mm or less downstream from the plate making start line in the sub-scanning direction), From images captured with a CCD camera through an optical microscope, Mitani Corporation
Using the image analysis package MacSCOPE, through holes in 100 perforations were cut out by binarization, and the SN ratio of the area of the through holes was determined.

The S / N ratio of the area of the through hole is the S / N ratio of the desired characteristic. The larger the value, the smaller the variation in the perforated area. The SN ratio of the perforated area is difficult to evaluate unitarily because the value differs depending on the measurement conditions.
In order to obtain a uniform transition state from each perforation, 10 db or more is actually necessary, and 13 db or more is desirable. If less than 10 db, the problem is considered to be large.

Evaluation Conditions of Printed Material In each of Examples and Comparative Examples, the obtained plate was manually applied to a printing drum, and printing was performed using a stencil printing machine RISOGRAPH (registered trademark) GR377 manufactured by Riso Kagaku Kogyo. Standard conditions (power supply O
This was performed using a lithographic ink GR-HD (trade name, manufactured by Riso Kagaku Kogyo Co., Ltd.) at N setting. The ambient temperature is room temperature (25 ° C.).

The uniformity of solids was evaluated by subjectively evaluating the degree of density variations due to microscopic (period of about 1 mm or less) locations caused by variations in the perforated shape in the solid portion of the printed matter. Indicated by the standard: ：: No density variation is felt at all, ：: There is slight density variation, but both solid reproducibility of character originals and tone reproducibility of photographic originals are acceptable, △: Text originals Has no problem with solid reproducibility, but the gradation reproducibility of the shadow portion of the photographic document is poor. ×: The density variation is remarkable, and the solid reproducibility of the text document and the gradation reproducibility of the photographic document are poor. .

The blurring of the fine characters is described in the subjective evaluation of the degree of blurring (loss of the pattern to be continuous) attributable to the variation of the perforated shape in the fine character portion of the printed matter. Is not felt, ○: There is a slight blur, but the reproducibility of fine characters (black characters on a white background) and the gradation reproducibility of the highlight part of a photo document are at a level where there is no problem. There is no problem with the reproducibility of fine characters (black characters on a white background), but the gradation reproducibility of the highlight part of the photo document is poor. ×: The blur is remarkable, and the fine characters of the character document (black characters on a white background)
, And the gradation reproducibility of the highlight portion of the photographic original are inferior.

[0093] Fine character crushing Fine character crushing indicates, in a subjective evaluation, the degree of crushing (deletion of a white background that should be between two adjacent patterns) due to variations in the perforated shape in the fine character portion of a printed matter. A: ◎: No crushing is felt at all, ：: Slight crushing, but there is no problem in the reproducibility of fine characters (white characters on black background) and the gradation reproducibility of shadows in photo documents , △: The reproducibility of fine characters (white characters on a black background) of a text document is not a problem, but the gradation reproducibility of the shadow portion of a photographic document is poor. White characters)
And the gradation reproducibility of the shadow portion of the photographic document are inferior.

[0094] smearing smearing, it backside of the printed material stacked by printing,
The degree of staining by the ink transferred to the print surface of the printed matter immediately before contact with the ink was evaluated by subjective evaluations according to the following criteria: ：: No set-off was observed at all, ○: Slight set-off was observed, but the solid portion was large. There is no problem even for documents with a large amount of ink transfer, which is an acceptable level for official printed matter. △: There is no problem in areas where the amount of ink transfer is small, such as fine characters (black characters on white background) and highlights, but large solids The stain is conspicuous in the portion where the transfer amount of the ink is large. Cannot be accepted as an official print, but can be used as an informal print. X: Offset is remarkable, and stains are conspicuous in almost all original parts. Unofficial prints are unacceptable.

Influence on the thermal head The effect on the thermal head is that the resin or adhesive component of the film sticks or burns in the vicinity of the heating element, or the applied heating of the heating element due to excessive applied energy or overheating of the heating element. Indicates the degree of deterioration (decrease in heat generation capacity). B4
After making a 500-plate version of a test pattern image with an image ratio of 33% of the size, an image for evaluation is made and printed, and the state of the plate and the image quality of the printed matter are evaluated. The vicinity of the heating element is observed with an optical microscope. The evaluation criteria are as follows: ：: The state of the plate making, the image quality of the printed matter, and the state near the heating element are all unchanged from the initial state after the plate making of the 500 plate. ：: Slight accumulation near the heating element. The material can be confirmed, but the amount is very small, and the plate making condition and the image quality of the printed material are the same as those after the 500 plate making and the initial condition. △: Deposits can be confirmed near the heating element, and the plate making condition and printed material The image quality of the 500 plate after plate making is deteriorated compared to the initial state. ×: A large amount of deposits can be confirmed in the vicinity of the heating element, or the heating capacity has been reduced due to the deterioration of the heating element. The plate making state and the image quality of the printed matter are significantly degraded in the state after the 500 plate making compared to the initial state.

(Comparative Example 1) When the resolution in the main scanning direction = the resolution in the sub-scanning direction = 300 dpi, the printing conditions were set such that the target value of the diameter of the through-hole was 60 μm in both the main scanning direction and the sub-scanning direction, and the heat-sensitive stencil sheet was made. And printed.

At this time, the height of the contour is larger than the value of the expression [1], and neither expression [1] nor expression [2] is satisfied.

(Example 1) The film thickness of Comparative Example 1 was
Plate making and printing were performed in the same manner as in Comparative Example 1, except that the thickness was reduced to 3.5 μm from 4.5 μm, and the applied energy was reduced accordingly. As a result, the volume of the resin at the location of the through hole was reduced, and the height of the contour was reduced.

At this time, both the formula [1] and the formula [2] were checked for the height of the contour.

(Example 2) The thickness of the film was
Plate making and printing were performed in the same manner as in Comparative Example 1 except that the thickness was reduced to 1.7 μm with respect to 4.5 μm, and the applied energy was reduced accordingly. As a result, the volume of the resin at the location of the through hole was reduced, and the height of the contour was reduced.

At this time, both the formula [1] and the formula [2] were checked for the height of the contour.

(Comparative Example 2) At a main scanning resolution of 300 dpi and a sub-scanning resolution of 400 dpi, printing conditions were set such that the target value of the diameter of the through-hole was 59 μm in the main scanning direction and 44 μm in the sub-scanning direction. Was made and printed.

At this time, the height of the contour in the main scanning direction is given by the following equation.
It is larger than the value of [2] and does not satisfy Equation [2].

(Example 3) The film thickness of Comparative Example 2 was
Plate making and printing were performed in the same manner as in Comparative Example 2 except that the thickness was reduced to 1.7 μm with respect to 4 μm, and the applied energy was reduced accordingly. As a result, the volume of the resin at the location of the through hole was reduced, and the height of the contour was reduced.

At this time, both the formula [1] and the formula [2] were used for the contour height.

(Comparative Example 3) When the resolution in the main scanning direction = the resolution in the sub-scanning direction = 400 dpi, the printing conditions were set assuming that the target value of the diameter of the through hole was 42.5 μm in both the main scanning direction and the sub-scanning direction. Plate making and printing.

At this time, the height of the contour in the main scanning direction is given by the following equation.
It is larger than the value of [2] and does not satisfy Equation [2].

(Example 4) The thickness of the film was
Plate making and printing were performed in the same manner as in Comparative Example 3 except that the thickness was reduced to 2.5 μm with respect to 4 μm, and the applied energy was reduced accordingly. As a result, the volume of the resin at the location of the through hole was reduced, and the height of the contour was reduced.

At this time, both the formula [1] and the formula [2] were used for the contour height.

(Example 5) The film thickness of Comparative Example 3 was
Plate making and printing were performed in the same manner as in Comparative Example 3, except that the thickness was reduced to 1.7 μm with respect to 4 μm, and the applied energy was reduced accordingly. As a result, the volume of the resin at the location of the through hole was reduced, and the height of the contour was reduced.

At this time, both the formula [1] and the formula [2] were checked for the height of the contour.

(Comparative Example 4) When the resolution in the main scanning direction = the resolution in the sub-scanning direction = 600 dpi, the printing conditions were set such that the target value of the diameter of the through-hole was 26 μm in both the main scanning direction and the sub-scanning direction, and the heat-sensitive stencil sheet was made. And printed.

At this time, the height of the contour in the main scanning direction is given by the following equation.
It is larger than the value of [2] and does not satisfy Equation [2].

(Example 6) The film thickness of Comparative Example 4 was
Plate making and printing were performed in the same manner as in Comparative Example 4 except that the thickness was reduced to 1.7 μm from 3.5 μm, and the applied energy was reduced accordingly. As a result, the volume of the resin at the location of the through hole was reduced, and the height of the contour was reduced.

At this time, both the formula [1] and the formula [2] were checked for the height of the contour.

[0116]

[Table 1]

[0117]

According to the present invention, when a stencil printing plate is produced by perforating a film of a heat-sensitive stencil sheet used for stencil printing using a heating device such as a thermal head, the heat transfer efficiency is reduced. It does not require large applied energy and high temperature conditions for the plate making device, and therefore improves the plate making conditions (reducing power consumption, shortening the plate making time, preventing deterioration of the heating element), and keeping the size of the perforations appropriate. Reduces variations in shape, thus improving image quality of printed matter (reducing density variations in solid areas, reducing blurring and crushing of fine characters, reducing set-off and strike-through), and film resin adheres to heating elements It is possible to realize a perforation form for preventing the operation from being performed.

[Brief description of the drawings]

FIG. 1 is a schematic plan view and a cross-sectional view of perforations formed in a film of a heat-shrinkable heat-sensitive stencil sheet.

FIG. 2 is a graph showing a temperature distribution of a heating element of the thermal head.

FIG. 3 is a graph showing a temperature distribution of a film heated by a heating element of a thermal head.

FIG. 4 is a graph showing the relationship between the temperature of the film of the heat-shrinkable heat-sensitive stencil sheet and the heat shrinkage stress.

FIG. 5 is a schematic plan view showing a moving direction of a resin when heat-perforating a film of a heat-shrinkable heat-sensitive stencil sheet.

FIG. 6 is a schematic plan view for explaining the perforation behavior of a film of a heat-shrinkable heat-sensitive stencil sheet under heat shrinkage and heat melting.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Perforation 2 ... Through-hole 3 ... Contour 4 ... Elliptical cross section 5 ... Thin film part 6 ... Reference plane 7 ... Contour height

Claims (4)

[Claims] 1. A stencil printing method in which a heat-shrinkable film of a heat-sensitive stencil sheet having a heat-shrinkable film is selectively heated by a heating device to form independent dot-like perforations corresponding to an image. Has a profile surrounding the through-hole, and the height h of the profile protruding on the heated side of the heat-shrinkable film relative to the film surface before perforation satisfies the following formulas [1] and [2] A method of making a heat-sensitive stencil sheet. h ≦ 4 [μm] [1 ] h ≦ 0.05√ (p x p y) [μm] [2] ( wherein, the pitch of the p _x in the main scanning [μm], p _y sub-scanning pitch [[mu] m] Is.) 2. A stencil making apparatus which selectively heats a heat-shrinkable film of a heat-sensitive stencil sheet having a heat-shrinkable film with a heating device to form independent dot-like perforations corresponding to an image. Has a profile surrounding the through-hole, and the height h of the profile protruding on the heated side of the heat-shrinkable film relative to the film surface before perforation satisfies the following formulas [1] and [2] A stencil making machine for heat-sensitive stencils. h ≦ 4 [μm] [1 ] h ≦ 0.05√ (p x p y) [μm] [2] ( wherein, the pitch of the p _x in the main scanning [μm], p _y sub-scanning pitch [[mu] m] Is.) 3. A stencil printing plate comprising a heat-shrinkable film in which independent dot-like perforations corresponding to an image are formed by being selectively heated by a heating device, wherein the perforations are contours surrounding the through-holes. The height h of the contour raised on the surface to be heated on the heat-shrinkable film with respect to the film surface before perforation.
Is a stencil printing plate characterized by satisfying the following expressions [1] and [2]. h ≦ 4 [μm] [1 ] h ≦ 0.05√ (p x p y) [μm] [2] ( wherein, the pitch of the p _x in the main scanning [μm], p _y sub-scanning pitch [[mu] m] Is.) 4. A heat-sensitive stencil sheet comprising a heat-shrinkable film selectively heated by a heating device to form independent dot-like perforations corresponding to an image, wherein the perforations have a contour surrounding the through-holes. A height h of a contour raised on a surface to be heated on the heat-shrinkable film with respect to a film surface before perforation satisfies the following formulas [1] and [2]. Base paper. h ≦ 4 [μm] [1 ] h ≦ 0.05√ (p x p y) [μm] [2] ( wherein, the pitch of the p _x in the main scanning [μm], p _y sub-scanning pitch [[mu] m] Is.)